A T N F    D a i l y    A s t r o n o m y    P i c t u r e

8th of March 2023
ATNF Colloquium
Galactic HII regions, diffuse ionised gas, and structure in the Milky Way
Trey Wenger (U. of Wisconsin-Madison)
Abstract: Radio recombination lines (RRLs) are an unobscured tracer of ionized gas in both the diffuse interstellar medium (ISM) as well as high-mass star-forming regions. The HII Region Discovery Surveys (HRDS) have nearly tripled the number of known high-mass star-forming regions in the Milky Way by detecting RRL emission toward infrared-identified HII region candidates. HII regions are the classic tracer of structure in galaxies, and their physical conditions (e.g., metallicity, internal kinematics) inform models of high-mass star formation and Galactic chemodynamical evolution. I will give a brief overview of our latest Australia Telescope Compact Array project, the Southern HII Region Discovery Survey, and some preliminary results with the first Galaxy-wide flux-limited HII region sample, including a novel technique to constrain the Milky Way morphological structure. We serendipitously discovered (1) a population of HII regions with ionized gas velocity gradients and (2) RRL emission from diffuse ionized gas. I will discuss these discoveries, their implications, and our follow-up work, which will inform both models of high-mass star formation as well as our understanding of the ISM and Galactic structure.

As part of a large Australia Telescope Compact Array (ATCA) project, the Southern HII Region Discovery Survey (SHRDS) serendipitously discovered ionized gas velocity gradients in a population of massive star forming regions. The figure above shows one such nebula, the HII region known as G297.651–00.973. The background color is a WISE three-color infrared image (22 micron in red, 12 micron in green, and 3.4 micron in blue), the black contours represent the SHRDS radio continuum brightness, and the colored contours represent the ionized gas velocity field. What is the origin and nature of these ionized gas velocity gradients? Follow-up work with the ATCA and the Very Large Array will hopefully answer these questions.

<<   |   archive   |   about   |   today   *   ATNF   |   Parkes   |   ATCA   |   Mopra   |   VLBI   |   ASKAP   |   >>